Over the last decade, many children who tragically died from flu were previously healthy kids, without chronic medical conditions, a new study finds.

Between 2004 and 2012, a total of 830 U.S. children died from flu, the study found. Of these, more than 40 percent did not have a medical condition such as asthma or heart disease that would put them at high risk for flu complications.

What's more, previously healthy children were nearly twice as likely to die from the flu before they were admitted to the hospital, or within three days of symptom onset, compared with children who had high-risk medical conditions and got the flu. [6 Flu Vaccine Myths]

The study underscores the fact that all children, regardless of age or pre-existing medical conditions, can potentially develop severe complications from the flu, the researchers said.

"Healthy kids are at risk, too. I think that's something that a lot of people don't recognize," said study researcher Dr. Karen Wong, of the Centers for Disease Control and Prevention (CDC). "People can get very sick very quickly, even if they don't have an underlying medical condition."

The findings highlight the importance of flu vaccination for all children ages 6 months and older, the researchers said. Of the 511 children who died and who were eligible for vaccination, just 16 percent had received a flu shot.

The findings also suggest that children who develop severe illness from the flu, who are hospitalized or who are at high risk for complications (such as those less than 2 years old) should receive treatment with antiviral drugs as soon as possible, the researchers said.

The study analyzed information on child flu deaths reported to the CDC. During the study period, the deadliest flu season for children was 2009 to 2010; over that time, 282 children died. The mildest flu season was 2011 to 2012, in which 35 deaths occurred.

The majority of deaths, 57 percent, occurred among children with high-risk medical conditions. Of these, the most commonly reported condition was a neurological disorder, such as cerebral palsy, with 33 percent of these children having a neurological condition. This was followed by lung disorders (26 percent), asthma (16 percent) and genetic disorders (12 percent).

It is especially important that children with high-risk medical conditions receive flu shots before flu season begins, the researchers said.

It's not clear why previously healthy children were at greater risk for death soon after symptom onset. But healthy kids were also more likely to have a bacterial infection along with their flu infection, which may have contributed to the differences in outcomes between the two groups, the researchers said.

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Rachael Rettner

Rachael has been with Live Science since 2010. She has a masters degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a Bachelor of Science in molecular biology and a Master of Science in biology from the University of California, San Diego.